In every system dedicated to the pneumatic transport of abrasive solid particles, a significant problem to be solved concerns the excessive wear of the pipelines. This is particularly true of large capacity high-temperature high-pressure systems. In order to avoid excessive wear, the lines must be straight (with any redirection, such as between vertical and horizontal, requiring specialized elbows). Any bend or deviation of the straight pipeline portions produces a point prone to abrasion and thus subject to rapid erosion through the wall of the pipeline. This is a particular problem where the carrier gas is flammable or a potential health concern, such as carbon monoxide.
When the pipeline is required to be straight and the system must also be operated under pressure and at high-temperature, the expansion of the pipes poses a further particularly difficult problem.
Many commercial solutions to compensate for the expansion of pipe lines show expansion joints that allow changes of position and usually are specified for non-solid fluids only, that is without entrained solids, at mid-range temperatures. These do not have the abrasion problems that solids transport present.
The prior art shows several embodiments related to coupling pipes at high-pressure which mainly compensate for the separative forces caused by the internal pressure, while others are related to systems allowing for movement between coupled pipelines.
U.S. Pat. No. 4,317,586 to Campbell shows a pressure-compensating pipe joint for pressure-variable fluid transport. The joint includes a sleeve 22 telescopically mated with and between the ends 12 and 13 of two conjoined pipes. The internal pressure within the pipes tending to separate the telescopic joint is compensated for by applying the same internal pressure on an equivalent area on piston heads in external cylinders acting between the conjoined pipe ends in a direction opposing separation. However, there is no teaching to tension the aligned pipes by a compensating force in excess of the separating force at the expansion joint. Also disclosed in this patent, is the capability of the joint to articulate and to permit relative movement of one pipe with respect to the other, including internal on rotational movement. This disclosure and embodiment is both insufficient and inappropriate to pneumatic transport of abrasive materials (where bending or alignment deviations of the pipes must be avoided). Another difference between U.S. Pat. No. 4,317,586 and the present invention is that when the fluid contained in the pipe further includes solid particles, any cavities in the articulating means should be avoided in order to reduce abrasion and jambing accumulation of the transported particles in said cavities.
U.S. Pat. No. 4,635,533 to Whiteside-II describes an expansion joint (used in petroleum FCC units for handling high temperature catalyst particles) to limit or counter-balance the separation of the joint under increasing pressure and/or to permit compensating contraction of a bellows coupling under increasing temperature. This system shows an embodiment that senses strain at an elbow in the piping to apply independent fluid pressure as a counter-thrust into the bellows at the adjacent pipe joint. This teaching is directed to compensate for the changes caused by the operating pressure and/or thermal expansion. Furthermore this compensating system described by Whiteside-II is used to maintain pipes and elbows with no strain no matter whether their temperature is high or low. Thus there is a teaching of compressing the joint 22 of the offset stain (by action of the structure 64 on rods 86), but no teaching of tensioning the pipes 26 or 32.
U.S. Pat. No. 2,545,701 to McCausland shows a compensated expansion joint directed to counteract the thrust forces caused by the internal pressure. This is very similar to the Campbell patent and is distinguishable for many of the same reasons. McCausland teaches that the expansion joint can be either slip-joint or corrugated bellows-type. Even though it is applicable for conveying fluids through the pipes and expansion joints, it does not suitably apply to the pneumatic transport of solid particles. When the thermal expansion is the main concern, it is desired that the longitudinal changes be freely compensated by means of the expansion joint. If solid particles are conveyed by the fluid circulating through the pipes, said particles will "see" a low velocity zone at the bellows thus settling on them, and resulting in additional resistance to the expansion or contraction of the joint.
Also of general background interest are U.S. Pat. No. 2,314,776 to Dittus et al.; U.S. Pat. No. 2,348,833 to Miller; U.S. Pat. No. 2,373,280 to Weber; U.S. Pat. No. 3,458,219 to Wesch; U.S. Pat. No. 4,146,253 to Celommi; U.S. Pat. No. 4,475,750 to Campbell; U.S. Pat. No. 4,482,171 to Campbell; U.S. Pat. No. 4,615,542 to Ideno et al.; and, U.S. Pat. No. 5,116,085 to Carrel. None of the above prior art however discloses the combination of features and advantages of the present invention.